Patient's Peak Skin Dose evaluation using Gafchromic films in interventional cardiology procedures and its correlation with other dose indicators.

OBJECTIVE: Number and complexity of interventional cardiology procedures have increased during last years and can result in patient skin dose high enough to cause deterministic skin effects. The aim of the work is to investigate the correlation between Peak Skin Dose (PSD) and the dosimetric indicators directly registered by the radiological equipment and provide the physicians a tool to identify patients at risk of deterministic effects and include them into a follow-up program. METHODS: PSD was measured in vivo using radiochromic Gafchromic XR-RV3 films, properly calibrated. DAP, Cumulative Dose at the interventional reference point (CD) and exposure time of each procedure were retrieved from the Radiation Dose Structured Reports created by an Allura Clarity Xper FD20 angiographic system. Linear correlation between PSD and both DAP and CD was investigated. RESULTS: 42 interventional cardiology procedures (16 CA and 26 PTCA) were involved in the study. The dosimetric indicators values for PTCA are generally higher than those for CA, due to the different levels of procedure complexity. Mean PSD values were (103 ±â€¯64) and (526 ±â€¯436) mGy for CA and PTCA procedures. For CA, we found strong correlation both between PSD and DAP (r = 0.753) and PSD and CD (r = 0.782). For PTCA, good correlation both for DAP (r = 0.648) and CD (r = 0.649) was found. CONCLUSIONS: DAP and CD show strong correlation with PSD measured with Gafchromic films during interventional procedures. The proposed method allows the physician to estimate patient's PSD from the dosimetric indicators that the radiological equipment display and record at the end of the procedure.

Red marrow and blood dosimetry in (131)I treatment of metastatic thyroid carcinoma: pre-treatment versus in-therapy results.

Treatment with radioiodine is a standard procedure for patients with well-differentiated thyroid cancer, but the main approach to the therapy is still empiric, consisting of the administration of fixed activities. A predictive individualized dosimetric study may represent an important tool for physicians to determine the best activity to prescribe. The aim of this work is to compare red marrow and blood absorbed dose values obtained in the pre-treatment (PT) dosimetry phase with those obtained in the in-treatment (IT) dosimetry phase in order to estimate the predictive power of PT trial doses and to determine if they can be used as a decision-making tool to safely administer higher (131)I activity to potentially increase the efficacy of treatment. The PT and IT dosimetry for 50 patients has been evaluated using three different dosimetric approaches. In all three approaches blood and red marrow doses, are calculated as the sum of two components, the dose from (131)I activity in the blood and the dose from (131)I activity located in the remainder of the body (i.e. the blood and whole-body contributions to the total dose). PT and IT dose values to blood and red marrow appear to be well correlated irrespective of the dosimetric approach used. Linear regression analyses of PT and IT total doses, for blood and red marrow, and the whole-body contribution to these doses, showed consistent best fit slope and correlation coefficient values of approximately 0.9 and 0.6, respectively: analyses of the blood dose contribution to the total doses also yielded similar values for the best fit slope but with correlation coefficient values of approximately 0.4 reflecting the greater variance in these dose estimates. These findings suggest that pre-treatment red marrow dose assessments may represent an important tool to personalize metastatic thyroid cancer treatment, removing the constraints of a fixed activity approach and permitting potentially more effective higher (131)I activities to be safely used in-treatment.

Modeling dose deposition and DNA damage due to low-energy ß(-) emitters.

One of the main issues of low-energy internal emitters concerns the very short ranges of the beta particles, versus the dimensions of the biological targets. Depending on the chemical form, the radionuclide may be more concentrated either in the cytoplasm or in the nucleus of the target cell. Consequently, since in most cases conventional dosimetry neglects this issue it may overestimate or underestimate the dose to the nucleus and hence the biological effects. To assess the magnitude of these deviations and to provide a realistic evaluation of the localized energy deposition by low-energy internal emitters, the biophysical track-structure code PARTRAC was used to calculate nuclear doses, DNA damage yields and fragmentation patterns for different localizations of radionuclides in human interphase fibroblasts. The nuclides considered in the simulations were tritium and nickel-63, which emit electrons with average energies of 5.7 (range in water of 0.42 µm) and 17 keV (range of 5 µm), respectively, covering both very short and medium ranges of beta-decay products. The simulation results showed that the largest deviations from the conventional dosimetry occur for inhomogeneously distributed short-range emitters. For uniformly distributed radionuclides selectively in the cytoplasm but excluded from the cell nucleus, the dose in the nucleus is 15% of the average dose in the cell in the case of tritium but 64% for nickel-63. Also, the numbers of double-strand breaks (DSBs) and the distributions of DNA fragments depend on subcellular localization of the radionuclides. In the low- and medium-dose regions investigated here, DSB numbers are proportional to the nuclear dose, with about 50 DSB/Gy for both studied nuclides. In addition, DSB numbers on specific chromosomes depend on the radionuclide localization in the cell as well, with chromosomes located more peripherally in the cell nucleus being more damaged by short-ranged emitters in cytoplasm compared with chromosomes located more centrally. These results illustrate the potential for over- or underestimating the risk associated with low-energy emitters, particularly for tritium intake, when their distribution at subcellular levels is not appropriately considered.